Terfenol-D | Hacker News Reader

Terfenol-D

en.wikipedia.org

90 pointsgraderjs24 comments

I have a box with samples of this somewhere behind me on my shelf. :) Been meaning to find some time to play with it.The samples came from: Extrema Products Inc. - Subsidiary of Edge technologies. I received a kit with a variety of little rods and a 1.5" or so disk.

I'm proud of everyone else that picked up on the piezo analogy! so cool! Here's a deeper look on the idea and the mass-change experiments:

https://owlcation.com/stem/What-is-the-Mass-Effect-Gravity-A...

edited to add video and sciAm paywall links:

https://www.youtube.com/watch?v=_INqXPFdJM8

https://www.scientificamerican.com/article/the-good-kind-of-...

Why is this (almost) at the top of HN? Nothing really stood out for me after a quick skim of the wiki page. Is there some additional context that I'm not aware of, or is this just a case of "huh, cool"?

Why is this (almost) at the top of HN? .... is this just a case of "huh, cool"?

That's why I upvoted indeed and it's one of the reasons HN is what it is. It's one of the welcome additions to the software- and hardware-related posts which, let's be honest, often go on and on about the same subject. Moreover if we're lucky someone here actually works in a field which uses this materail and can bring up interesting stories.

Fully agree. The best HN posts are the ones where a few experts in an esoteric field can totally geek out about their art. I may not understand half of what they say but it's always fully interesting.

Is this the magnetic complement of the piezo-electric sensor/actuator?

Yes.

> The alloy has the highest magnetostriction of any alloy, up to 0.002 m/m at saturation; it expands and contracts in a magnetic field.

I think that would be electrostriction <=> magnetostriction. The ...striction effects are non-linear, while piezo... is linear.

...striction effects are linear. Piezo elements are electrostriction. This material is used instead of piezo in deep sea sonars because it can work at higher pressures.

Does this material also produce a magnetic field when stressed?

Stuff like is what adds up to make USA submarine technology probably the most superior tech in the world.

How does it generate low frequencies? And what are the properties of low frequency sonar?

I've been working with voice coil tactile speakers and it is HARD to make powerful low frequencies.

0.002 m/m doesn't sound very much. I was imagining something that visibly changes shape in a magnetic field, like some kind of magnetic magic goo...

I wonder, how strong, physically, is it? I mean, what’s the formula for computing the mechanical force it can actuate with, compared to eg an electromagnet?

Perhaps something that could be used in the MEGA drive.

Had to look up what you meant but I think it's this: https://medium.com/predict/mega-drive-the-tech-that-promises...

To clarify: to people outside North America "Mega Drive" normally refers to the Sega Genesis gaming console.

It's a violation of the conservation of momentum; it's extremely unlikely to be real.

General relativity does not conserve energy.

Ok, I’ll bite: how do we manipulate local nonrelativistic spacetime curvature near a spaceship to take advantage of the magnetorestrictive properties of this material? I’ve just finished my last undergrad-equivalent course GR, so voice this in the appropriate math.

throw when heavy, pull when light. its crazy.

https://www.scientificamerican.com/article/the-good-kind-of-...

https://owlcation.com/stem/What-is-the-Mass-Effect-Gravity-A...

You linked to ... woo? Like, this is not even science. I asked for a mathematical explanation of how to utilize the more exotic invariants of momentum in nonrelativistic spacetime, voiced in terms of GR. If the GP is going to claim this drive is possible because momentum isn't conserved in GR, the least they could do is use GR to show what they mean?

It's a low bar, but it's there.

https://en.wikipedia.org/wiki/Mach%27s_principle

Enjoy.

Hmm! I didn't realize that, and I also didn't realize that in a relativistic theory conservation of energy and momentum are the same thing.

(Evidently some dumbfucks are downvoting your comment instead of checking Wikipedia.)

What.

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